Laser image display apparatus

ABSTRACT

A light diffuser containing light diffusing elements is arranged in the most appropriate position between a spatial light modulator and an illumination optical system. Thereby, particles as light diffusing elements diffuse rays of light emitted from a laser light source. Accordingly, indefinite numbers of speckle pattern are formed so that, for example, a speckle noise which occurs on an image projected to a screen is reduced. As a result, loss of light amount after light diffusion is suppressed to small amount, and thereby a laser image display apparatus capable of displaying a bright and high-quality image having no luminosity irregularity is provided.

TECHNICAL FIELD

The present invention relates to an image display apparatus using alaser as a light source. More particularly, it pertains to a laser imagedisplay apparatus comprising means for reducing speckle noises whichappears on a display.

BACKGROUND ART

FIG. 7 shows a schematic construction of a conventional laser display.At first, rays of light emitted from laser light sources 101 a-101 cincluding three RGB colors (R: red, G: green, B: blue) are beam-expandedby an expander optical system 102 including collective lens 109 a-109 c.Next, expanded light rays are beam-formed by an integrator opticalsystem including lenses and arrays of small lenses to provide a uniformillumination to a spatial light modulator 105. Herein, field lenses 104a-104 c are adapted for converting the rays of light having been passedthrough the spatial light modulators 105 a-105 c into collected orcollected light rays so as to make rays of light pass through anaperture of a projection lens 107 efficiently.

Then, an intensity modulation is executed to the beam-formed rays oflight in the spatial light modulators 105 a-105 c in response to aninput image signal, and the rays of light are combined in a dichroicprism 106. A combined ray of light is diverged in the projection lens107 and projected to a screen 108. Accordingly, a two-dimensional imageis displayed on the screen 108. In the display having this construction,the light sources for RGB respectively emit single color lights.Accordingly, an image having high color purity and brightness can bedisplayed by using laser light sources having appropriate wavelength.

However, such display has a problem of the so-called speckle noise whichis likely to occur due to use of a laser light source having highcoherency. The speckle noise is fine irregular noises which occur whenrays of laser light are diffused on the screen 8 and the diffused lightrays on respective portions of the screen 8 interfere with each other.

Conventionally, as disclosed in Patent Document 1, the speckle noise iseliminated by operating a motor 110 to oscillate a screen 108 or, asdisclosed in Patent Document 2, by applying an external force tooscillate/rotate a diffuser. These methods change the speckle patternwithin a time segment shorter than a display changing time which enablesthe human to see to average out a speckle pattern so that the observercannot see the speckle noise. Further, Patent Document 3 discloses amethod which prevents the speckle noise by changing a state ofpolarization of a laser light in a time frame and projects the laserlight to a screen on which particles made of anisotropic crystals areapplied.

Further, as described in Patent Document 4, the speckle noise can bereduced also by using a mobile diffuser, but there is a problem ofnoises such as motor driving sounds generated at the time when thediffuser is operated. To prevent sound noises caused by operation of amotor and the like, accordingly, Patent Document 5 discloses a methodwhich prevents the speckle noise at a low cost without mechanicaloperation using a light diffusing optical system where microparticlesare contained in a cell and the microparticles are electricallyoscillated. However, in the case of using the speckle reducing methoddisclosed in Patent Document 5, the light rays diffused in the diffuseroptical system are more likely to partially come outside of an imagedisplay area of the spatial light modulator as the distance between thespatial light modulator and the diffuser optical system becomes longer.As a result, the loss in the light intensity becomes larger, and thebrightness of the screen lowers.

Furthermore, in the case of the diffuser optical system usingmicroparticles, the microparticles in the cell are deviated so that alocal diffusing angle and transmittance efficiency in the diffuseroptical system differs at different locations. Therefore, as thedistance between the diffuser optical system and the spatial lightmodulator comes closer, this deviated distribution of transmittanceefficiency causes localization (luminosity irregularity) of lightintensity on the spatial light modulator. The luminosity irregularitymoves on the projection display following a movement of the diffuseroptical system, and consequently runs over an image. Accordingly, inorder to suppress image deterioration due to the luminosityirregularity, it is necessary to arrange the diffuser apart from thespatial light modulator with a predetermined distance.

In other words, speckle noise prevention optical systems, typicallydiffuser optical systems using microparticles, cannot eliminate thespeckle noise and realize a high-resolution, bright image having noluminosity irregularity if the optical system is not set in anappropriate position with respect to the spatial light modulator.However, an appropriate positional relationship between the diffuseroptical system and the spatial light modulator has not been discusseduntil now.

Patent Document 1:

Japanese Unexamined Patent Publication No. Sho55-65940

Patent Document 2:

Japanese Unexamined Patent Publication No. Hei6-208089

Patent Document 3:

Japanese Unexamined Patent Publication No. Hei3-109591

Patent Document 4:

Japanese Unexamined Patent Publication No. 2003-98476

Patent Document 5:

Japanese Unexamined Patent Publication No. Heill-218726

DISCLOSURE OF THE INVENTION

In view thereof, an object of the present invention is to solve theproblems, and provide a laser image display apparatus which canefficiently reduce an inherent speckle noise appearing in the case wherea coherent light source such as a laser source and the like is used, andrealizes a bright and high-quality image having no luminosityirregularity.

To achieve this object, the laser image display apparatus according toan embodiment of the present invention comprises: a laser light source;a light diffuser containing light diffusing elements, the lightdiffusing elements moving, swaying or oscillating; an illuminationoptical system which irradiates rays of light from the laser lightsource to the light diffuser; a spatial light modulator which isarranged near the light diffuser and irradiated by rays of lightdiffused by the light diffuser to produce image; and a projection lenswhich projects to a predetermined plane in space an image produced bythe spatial light modulator, wherein a light diffusing angle θ of thelight diffuser, a pitch P of transmission irregularity generated in thelight scattering means, a numerical aperture NA of the illuminationoptical system, and a distance L between the spatial light modulator andthe light diffuser have a relationship of P<2×tan(θ/2+Sin⁻¹(NA))×L.

With this construction, a ray of light emitted from the laser lightsource is irradiated to the light diffuser from the illumination opticalsystem. Light diffusing elements are enclosed in the light diffuser, andthe ray of light irradiated from the illumination optical system isdiffused by the light diffusing elements. At this time, the lightdiffusing elements are moved, swayed or oscillated so that a phasepattern of the diffused rays of light changes instantly, and thereby aspeckle pattern also changes. In other words, since different specklepatterns occur at each moment and these speckle patterns are timelyaveraged out at the time when an image projected to a particular planevia a spatial light modulator and a projection lens is observed, ahigh-quality two-dimensional image having a suppressed speckle noise canbe obtained.

Further, divergence of the incident ray of light irradiated from theillumination optical system to the light diffuser is expressed byθ/2+Sin⁻¹(NA) if it is assumed that a numerical aperture of theillumination optical system is NA and a full angle of a light diffusingangle of the light diffuser is θ. Accordingly, if a distance between thelight diffuser and the spatial light modulator is L, divergence of theray of light on the spatial light modulator can be expressed by2×tan(θ/2+Sin⁻¹(NA))×L. If the divergence is larger than a pitch P of atransmittance irregularity (luminous irregularity of a transmitted lightray) generated in the light diffuser, rays of light forming irregularityadjacent to each other are diffused and overlap with each other.Consequently, lowering of an image quality due to an irregularity can besuppressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an embodiment 1 of a laser imagedisplay apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a component of a laser imagedisplay apparatus of the present invention including an electrophoreticdiffuser in an embodiment 1.

FIG. 3 is a diagram showing divergence of rays of light to be diffusedby an electrophoretic diffuser 10 in an embodiment 1 of a laser imagedisplay apparatus of the present invention.

FIG. 4 is a schematic diagram showing an optical system formed byunifying an electrophoretic diffuser and a spatial light modulator in anembodiment 2 of a laser image display apparatus of the presentinvention.

FIG. 5 is a schematic diagram showing an optical system formed byunifying an electrophoretic diffuser and a reflective liquid crystalcomponent in an embodiment 2 of a laser image display apparatus of thepresent invention.

FIG. 6 is a schematic diagram showing an optical system having acombination of function of a diffuser and a spatial light modulator inthe embodiment 3 of a laser image display apparatus of the presentinvention.

FIG. 7 is a schematic diagram showing a conventional laser display.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are now described with reference tothe drawings.

Embodiment 1

FIG. 1 shows a schematic diagram of a laser image display apparatusaccording to an embodiment of the present invention. Rays of lightemitted from a red laser light source 1 a, a green laser light source 1b, and a blue laser light source 1 c are collected by collective lens 9a, 9 b and 9 c respectively. The collected rays of light are irradiatedto electrophoretic diffusers (light diffusers) 10 a, 10 b, 10 crespectively after being passed through an expander optical system 2 andan integrator optical system (illumination optical system) 3 and arebeam-shaped to have a uniform light intensity distribution. The rays oflight irradiated to the electrophoretic diffusers 10 a, 10 b, 10 c arediffused by diffusing elements contained. therein. Consequently,directions of the rays of light after being passed through theelectrophoretic diffuser 10 a, 10 b, 10 c are diffused.

The rays of laser light diffused by the electrophoretic diffusers 10 a,10 b, 10 c are irradiated to spatial light modulators 5 a, 5 b, 5 cincluding a liquid crystal panel and the like, for example, to produce atwo-dimensional image. The rays of light after being passed through therespective spatial light modulators 5 a, 5 b, 5 c are combined in adichroic prism and projected to a screen 8 by a projection lens 7.

Herein, field lens 4 a, 4 b, 4 c are adapted for converting the rays oflight having been passed through the spatial light modulators 5 a to 5 cinto collected beams to pass the rays of light through an aperture ofthe projection lens efficiently. As the laser light sources, 1 a, 1 b,and 1 c, further, a gas laser such as He—Ne laser, He—Cd laser and Arlaser, a semi-conductor laser such as AlGaln laser and GaN laser, or anSHG laser having solid laser as basic wave are used.

A speckle suppression operation of the laser image display apparatusincluding the construction shown in FIG. 1 is described with referenceto FIG. 2. FIG. 2 is a schematic diagram showing an optical system ofthe laser image display apparatus shown in FIG. 1 for one color. Forsimplicity, the expander optical system, the integrator optical system,the field lens and the dichroic prism are omitted. The rays of lightwhich have emitted from the laser light source 1 and passed through theintegrator optical system are formed into a light beam on theelectrophoretic diffuser 10 having a uniform intensity distribution. Thelight beam is diffused in the electrophoretic diffuser 10 and irradiatedto the spatial light modulator 5 at a uniform intensity distribution.The rays of light are applied with an intensity modulation by thespatial light modulator 5, and passed through the projection lens 7 sothat an expanded image is projected to the screen 8.

Here, it should be noted that there is the possibility that a specklenoise appears on an image projected to the screen 8 at a given time.However, in the course where the light beam passes through theelectrophoretic diffuser 10, electrophoretic elements A14 orelectrophoretic elements A15 contained in an aqueous solution 13 assolvent 13 in the electrophoretic diffuser diffuse the light beam sothat the phase pattern of the rays of light after being passed throughthe electrophoretic diffuser 10 changes. Accordingly, the pattern ofspeckle noise occurring in the image on the screen 8 also changes. Inthis embodiment, as the light diffusing particles contained in theelectrophoretic diffuser are used particles which are able to move, swayor oscillate owing to application of a voltage, for example, particlesincluding TiBaO₃ and the like which is able to undergo inducedpolarization. Such particles are referred to as migration particleshereinafter.

In this case, electrodes 11 are formed at both ends of theelectrophoretic diffuser, and an alternating voltage is applied to theelectrodes 11, and thereby migration particles in the electrophoreticdiffuser move, sway or oscillate in response to modulated frequenciesand the like of the alternating voltage. Consequently, the distributionof migration particles in a given plane in the electrophoretic diffuserchanges at each moment, and thereby the speckle pattern appearingchanges at each moment. In other words, since a different specklepattern appears at each moment, the speckle patterns are averaged out atthe time of observing a projected image, which makes it possible toobserve a two-dimensional image having suppressed speckle noise. It willbe seen that the greater the modulated frequency of the alternatingvoltage or the changing width of the alternating voltage to allowmigration particles in the electrophoretic diffuser 10 to move, sway oroscillate is made, the greater the spatial distribution ofelectrophoretic particles in the electrophoretic diffuser 10 changes.Consequently, the averaged speckle noise, which is sensed by human'seyes, can be more suppressed.

To use the electrophoretic diffuser effectively, further, it isnecessary to specify a distance between the electrophoretic diffuser 10and the spatial modulator 5 other than the above-described moving speeddetermined mainly by the modulated frequency. FIG. 3 is a diagramshowing a divergence of rays of light diffused by the electrophoreticdiffuser 10 in the embodiment 1 of the laser image display apparatus.

Assuming that the numerical aperture of the integrator optical system 3is NA, a divergence of rays of light irradiated from the integratoroptical system 3 to the electrophoretic diffuser 10 is expressed bySin⁻¹(NA) regardless of light incidence positions of the electrophoreticdiffuser 10. The bean of light is shown in a phantom line as lightbefore being diffused in this figure. Assuming that the full diffusingangle of the electrophoretic diffuser 10 is θ, the beam of light (shownby the phantom line in the figure) is diffused θ/2 conically withrespect to an axis of the beam of light before being diffused by theelectrophoretic diffuser 10. Consequently, the divergence angle of raysof light having been passed through the electrophoretic diffuser 10 isadded with a further divergence angle of θ/2, and thus expressed byθ/2+Sin⁻¹(NA).

Assuming that a distance between the electrophoretic diffuser 10 and thespatial light modulator 5 is L, accordingly, the divergence of light onthe spatial light modulator 5 is expressed by 2×tan(θ/2+Sin⁻¹(NA))×L.Here, the numerical aperture NA of the integrator optical system 3 isdetermined depending upon a numerical aperture of the projection lens 7.Since a projection lens 7 having a large numerical aperture is expensivein general, a projection lens 7 having a small numerical aperture isused in order to bring down costs. Generally, a projection lens havingan F value of 1.4 to 2.0 and a numerical aperture of 0.25 to 0.36 isused. Therefore, regardless as to whether or not there is provided theelectrophoretic diffuser 10, a numerical aperture NA of the integratoroptical system 3 needs to be smaller value than that of the projectionlens.

If a distance between the electrophoretic diffuser 10 and the spatiallight modulator 5 is larger than a certain limit, a part of the rays oflight diffused by the electrophoretic diffuser 10 comes outside of animage display area of the spatial light modulator 5, which results in alarger loss in the light amount, and thereby lowers the brightness onthe screen. In order to suppress the loss in the light amount lower thana certain amount, as shown in FIG. 3, the light diffusing angle θ of theelectrophoretic diffuser 10 is set so as to satisfy the followingequation:tan(θ/2+Sin⁻¹(NA))×L<D/3   (1)Wherein: NA denotes a numerical aperture of the integrator opticalsystem 3 (an illumination optical system using a light integrator); Ldenotes a distance between the electrophoretic diffuser 10 and thespatial light modulator 5; and D denotes a diagonal distance of an imagedisplay area of the spatial light modulator.

Herein, since the rays of light diffused to the spatial light modulator5 is not in connection with the light amount loss, the light divergenceshown in the left term of Equation 1 is half the above-mentioned lightdivergence on the spatial light modulator 5.

The light divergence shown in the left term of Equation 1 increasesmonotonously as the distance L between the electrophoretic diffuser 10and the spatial light modulator 5 increases, and the brightness on thescreen decreases. Further, in the case of using a laser light sourcehaving an ordinary brightness and an optical system having theconstruction shown in FIG. 1, the allowable brightness range where aperson can recognize an image on the screen 8 without sense ofdiscomfort is considered to be not lower than 25% of the brightness ofthe rays of light incidence to the electrophoretic diffuser 10. In otherwords, if the brightness is lower than 25%, an image on the screen 8becomes so dark. Therefore, it is necessary to increase the power of thelight source or suppress the light amount loss. Suppression of the lightamount loss to 75% or lower (i.e., 25% of the irradiated light incidenceto the spatial light modulator 5) can be achieved by setting the lightdivergence smaller than one-third (i.e., D/3) of the diagonal distanceof the image display area of the spatial light modulator 5.

In the following paragraphs of the specification, the value of NA doesnot indicate a determined value under an ideal condition, but asubstantial value including an error occurred at the time ofmanufacturing optical systems constituting the integrator optical system3 and a displacement occurred at the time of placing the integratoroptical system 3. In other words, for example, even though it isdesigned to have NA=0.2, values near 0.2, such as 0.19 and 0.22, are notexcluded.

In the case of using an electrophoretic diffuser 10 having a deviatedspatial distribution of migration particles, a local diffusing angle anda transmittance differ depending on a position in the electrophoreticdiffuser 10. Therefore, a deviated light intensity distribution occurson the spatial light modulator 5 due to a transmittance deviation as theelectrophoretic diffuser 10 is arranged improperly near the spatiallight modulator 5. A luminous irregularity moves on the projectionscreen following movement of migration particles contained in theelectrophoretic diffuser 10, and comes into a projected image. Toprevent this, the electrophoretic diffuser 10 is arranged apart from thespatial light modulator 5 a predetermined distance. The electrophoreticdiffuser 10 is irradiated in different directions from the respectiveelement lenses of the integrator optical system 3. Therefore, asufficient distance L between the electrophoretic diffuser 10 and thespatial light modulator 5 is effective to equalize luminousirregularities of light irradiated from the respective element lenses.

Particularly, the light diffusing angle θ of the electrophoreticdiffuser 10, a pitch P denoting a luminosity irregularity (transmissionirregularity) of the transmitted light on a side of the electrophoreticdiffuser 10 facing the spatial light modulator 5, and a distance Lbetween the electrophoretic diffuser 10 and the spatial light modulator5 are set so as to be in a relationship of2×tan(θ/2+Sin⁻¹(NA))×L   (2)depending on the numerical aperture NA of the integrator optical system3. In FIG. 3, a portion having the highest brightness of transmittedlight rays on a side of the electrophoretic diffuser 10 facing thespatial light modulator 5 is shown in a solid line running on theelectrophoretic diffuser 10 in a lateral direction(y-direction). Aninterval between portions having highest brightness aligned in alongitudinal direction is a pitch P denoting an irregularity. Normally,irregularity occurs also in a lateral direction (y-direction), but it isomitted in this figure for simplicity. Further, in FIG. 3, a lengthwhich is the same as the length of a pitch P on the electrophoreticdiffuser 10 is also shown on the spatial light modulator 5 by a lateral(y-direction) solid line. Furthermore, a portion which has an equaldistance to solid lines is shown by a dotted line.

If a divergence of the rays of light after being diffused on the spatiallight modulator 5 is larger than the pitch P denoting the irregularityof the transmitted light rays, the adjacent rays of light formingirregularity diffuses, and the diffusing rays thereby overlap with eachother. In other words, the conditions which satisfy the Equation 2suppress deterioration of an image quality due to an irregularity.

Further, though it is described above that the pitch P of theirregularity of the transmitted light rays is constant, the value of thepitch does not have to be constant and it can be varied. In such a case,an average of a plurality of values of the pitch P (for example, anarithmetic average) can be newly set as a new constant pitch P.

Furthermore, with reference to the Equation 1 and the Equation 2, it ispreferable to set the distance L between the electrophoretic diffuser 10and the spatial light modulator 5 within a range ofP/tan(θ/2+Sin⁻¹(NA))/2<L<D/tan(θ/2+Sin⁻¹(NA))/3.   (3)Normally, the irregularity pitch P of the rays of transmitted lightthrough the diffuser is smaller than 10 times of diameter d of particlesin the diffuser. Thus, if the integrator optical system 3 having anumerical aperture of 0.1 is used for example, it should have thedistance of 0.26 mm to 2.6 mm or more depending on the particle diameter(10 μm to 100 μm) of the migration particles contained in the diffuser.

Further, though the electrophoresis is used as a means for moving themigration particles in the present embodiment, a heat, a sound wave or amagnetism can be also used as a means for moving, swaying andoscillating the diffusing element to obtain a similar effect.Furthermore, the similar effect can be also obtained by moving, swayingor oscillating a solvent contained with the light diffusing elements.

Further, with regard to the light diffusing elements to be contained, iftwo or more kinds of particles having different characteristics from oneanother are mixed, e.g., the particles differ in the moving speed fromone another, the spatial distribution of the particles becomes morecomplicated. Consequently, more numbers of a phase patterns of lightbeam after being passed through the diffuser are formed, and a number ofthe speckle pattern increases. Thus, mixing particles having two or morekinds of characteristics is effective to reduce a speckle noise. Forexample, in the case where the diffuser described above is constructedby a liquid crystal, two or more kinds of liquid crystal havingdifferent polarization from one another contained in the diffuser makesdifferent response speed at the time of applying an electric field.Consequently, various diffusing light patterns and a large number ofspeckle patterns are formed, which effectively reduces the specklenoise.

Further, a particle used as a light diffusing element has, other thanthe polarization described above, characteristics such as size, mass anddensity. For example, in the case where particles having the samepolarization and density but having different size from one another arecontained, small particles move fast and large particles move slowlyrelative to the small particles at the time when a voltage is applied.In any of the cases above, the particles can have different movingspeeds, and thereby the speckle noise can be reduced.

For another example, in the case of using different kinds of migrationparticles, since the respective response speeds of particles withrespect to the electric field differ from one another, more irregularand complicated states of diffusion can be generated as compared to thecase of containing one kind of migration particles. Since containing theparticles having different response speed depending on an electronic ormagnetic effect of particles makes the spatial distribution of particlesin the diffuser more complicated , the similar effect with respect tospeckle noise reduction can be obtained.

Other than the above, making a moving (swaying, oscillating) speed and amoving (swaying, oscillating) direction of particles random is alsoeffective to generate an irregular diffusion. For example, the spatialdistribution of particles in the electrophoretic diffuser 10 can be mademore complicated and varied dividing an electrode 11 (transparentelectrode,) arranged on the electrophoretic diffuser 10 in some numbersand control each electrode with electric field separately, by formingthe divided electrodes 11 to have different shapes from one another andperform electric field control and by arranging another electrode notonly to upper and lower sides of the electrode 11 but also on front andfar side and perform an electric field control to the electrophoreticdiffuser 10 shown in FIG. 2, and thereby the reduction rate of thespeckle noise increases. Further, it is not necessary to arrange theelectrode described above on the same plane like the electrode 11 shownin FIG. 2, but it may be formed on a plane having a step.

According to the feature of the laser image display apparatus of thepresent invention, the screen 8 and the electrophoretic diffuser 10 arenot oscillated or moved and a sound caused by movement and oscillationis not generated. Accordingly, a quiet laser image display apparatus canbe realized.

In the above, the embodiment of the present invention is described withreference to the drawings showing a projection-type display havingseparated bodies of the projection optical system and the screen.However, the embodiment in the present invention can be applied to arear-projection type image display apparatus having a combination of aprojection optical system and a transparent screen; and atwo-dimensional image display apparatus having a type of directlyobserving the spatial light modulator irradiated by a laser from a rearside (for example, liquid crystal television which is now commerciallyavailable).

Further, the embodiment was described with reference to a displayapparatus of a color image, but the present invention can be used for animage projection apparatus having a single laser, for example, exposurelighting system used for a semiconductor process. As a spatial lightmodulator in the exposure lighting system, a photo mask and the like,for example, which is formed by patterning a metal film on a glassmotherboard is used and a mask pattern image is formed using asemiconductor motherboard as a screen.

Embodiment 2

Further, according to another construction of a laser image displayapparatus of the present invention, an electrophoretic diffuser 10containing light diffusing elements is unified with a spatial lightmodulator 5 as shown in FIG. 4, and thereby a speckle noise is reducedand eliminated. Herein, the optical system such as the integratoroptical system 3 and the like are omitted for simplicity. According tothis construction, after the rays of light emitted from the light sourcehaving been passed through the expander optical system and theintegrator optical system, rays of the light beam can be irradiated tothe unified optical system including the electrophoretic diffuser 10 andthe spatial light modulator 5 in a state of a uniform illumination lightray. Furthermore, as shown in FIG. 5, it can also be constructed so asto have a reflective spatial light modulator as a spatial lightmodulator. Here, LCOS (Liquid Crystal On Silicon), which isrepresentative of all other reflective liquid crystal 16, is used as areflective spatial light modulator. Furthermore, other than the above,if a ferroelectric liquid crystal is used as a reflective liquidcrystal, a response speed of a liquid crystal can be made faster andthereby an image having less afterimage can be projected.

Embodiment 3

Further, according to another construction of a laser image displayapparatus of the present invention, as shown in FIG. 6, a light diffusercontaining light diffusing elements and a liquid crystal used in atwo-dimensional spatial light modulator for projecting an image arecontained in the same liquid. For example, it functions as a diffuser bymoving the particles by heat, and, on the other hand, it functions as atwo-dimensional light modulator by controlling a liquid crystal (areflective liquid crystal is used in FIG. 6) by electricity.

Here, the same as in the embodiment 1, a distance between the diffuserand the light modulator needs to be set in an appropriate position tosuppress the light amount loss and the luminosity irregularity to aminimum. Therefore, portions of a light diffusing function and a lightmodulating function needs to be separated, and the particles and theliquid crystal contained in the same liquid needs to be arranged in anappropriate position.

Other Preferable Embodiment

FIG. 4 and FIG. 5 shows an electrophoretic diffuser 10 as one form ofthe diffuser. However, the diffuser in the embodiment of the presentinvention is not limited to it, but it can take a form of containinglight diffusing elements which are moved, swayed or oscillated byapplying a heat, a sound wave or an electric field. At that time, forexample, it is preferable that the light diffusing elements include morethan two kinds of materials having different characteristics such assize, mass, intensity or magnetic moment from one another.

General Outline of Embodiment

A general outline of an embodiment of the present invention is describedbelow.

(1) As described above, it is preferable that a laser image displayapparatus in the present invention comprises: a laser light source; alight diffuser containing light diffusing elements, the light diffusingelements moving, swaying or oscillating; an illumination optical systemwhich irradiates rays of light from the laser light source to the lightdiffuser; a spatial light modulator which is arranged near the lightdiffuser and irradiated rays of light diffused by the light diffuser toproduce image; and a projection lens which projects to a predeterminedplane in space an image produced by the spatial light modulator, whereina light diffusing angle θ of the light diffuser, a pitch P oftransmission irregularity generated in the light scattering means, anumerical aperture NA of the illumination optical system, and a distanceL between the spatial light modulator and the light diffuser have arelationship of P<2×tan(θ/2+Sin⁻¹(NA))×L.

According to this construction, rays of light emitted from the laserlight source are irradiated from the illumination optical system to thelight diffuser. Light diffusing elements are contained in the lightdiffuser, and the rays of light irradiated from the illumination opticalsystem are diffused by the light diffusing elements. At this time, sincethe light diffusing elements are moved, swayed or oscillated, a phasepattern of the diffused rays changes at each moment, and thereby aspeckle pattern changes. In other words, since different specklepatterns occur at each moment. These speckle patterns are timelyaveraged out at the time when an image projected to a particular planevia a spatial light modulator and a projection lens is observed.Accordingly, a high-quality two-dimensional image with a suppressedspeckle noise can be obtained.

Further, divergence of the ray of light irradiated from the illuminationoptical system to the light diffuser is expressed by Sin⁻¹(NA). Assumingthat a full angle of a light diffusing angle of the light diffuser is θ, a further divergence angle of θ/2 is added, and thereby a divergenceangle of light rays is expressed by θ/2+Sin⁻¹(NA). Accordingly, if alength between the light diffuser and the spatial light modulator is L,a divergence of the ray of light on the spatial light modulator can beexpressed by 2×tan(θ/2+Sin⁻¹(NA))×L. If the divergence is larger than apitch P of a transmittance irregularity (luminosity irregularity of atransmitted light ray) generated in the light diffuser, the adjacentrays of light forming irregularity diffuses, and the diffusing raysthereby overlap with each other. According to this, lowering of an imagequality due to an irregularity can be suppressed.

(2) A laser image display apparatus according to the laser image displayapparatus (1), wherein it is preferable that a light diffusing angle θof the light diffuser, a numerical aperture NA of the illuminationoptical system, a distance L between the spatial light modulator and thelight diffuser and a diagonal screen size D of the spatial lightmodulator have a relationship of tan(θ/2+Sin⁻¹(NA))×L<D/3.

According to this construction, since a divergence of the rays of lightafter being diffused on the spatial light modulator is larger than apitch P denoting an irregularity of the transmitted light rays, theadjacent rays of light forming irregularity diffuses, and thereby therays overlap with each other. Accordingly, a deterioration of an imagequality due to an irregularity can be suppressed. Further, since a halfof a light divergence on the spatial light modulator is set smaller thanone-third (i.e., D/3) of the diagonal distance of the image display areaof the spatial modulator, the amount of light not entering the spatiallight modulator (loss in the light amount) can be suppressed to 75% orlower. Accordingly, an image projected to the predetermined plane on ascreen and the like can be recognized without sense of discomfort.

(3) As described above, it is preferable that the laser image displayapparatus in the present invention comprises: a laser light source; alight diffuser containing light diffusing elements, the light diffusingelements moving, swaying or oscillating; an illumination optical systemwhich irradiates rays of light from the laser light source to the lightdiffuser; a spatial light modulator which is arranged near the lightdiffuser and irradiated by rays of light diffused by the light diffuserto produce image; and a projection lens which projects to apredetermined plane in space an image produced by the spatial lightmodulator, wherein a light diffusing angle θ of the light diffuser, anumerical aperture NA of the illumination optical system, a distance Lbetween the spatial light modulator and the light diffuser and adiagonal screen size D of the spatial light modulator have arelationship of tan(θ/2+Sin⁻¹(NA))×L <D/3.

According to this construction, rays of light emitted from the laserlight source are irradiated from the illumination optical system to thelight diffuser. Light diffusing elements are contained in the lightdiffuser, and the rays of light irradiated from the illumination opticalsystem are diffused by the light diffusing elements. At this time, sincethe light diffusing elements are moved, swayed or oscillated, a phasepattern of the diffused rays changes at each moment, and thereby aspeckle pattern changes. In other words, since different specklepatterns are generated and these speckle patterns are timely averagedout at the time when an image projected to a particular plane via aspatial light modulator and a projection lens is observed, ahigh-quality two-dimensional image with a suppressed speckle noise canbe obtained.

Further, divergence of the incident light rays from the illuminationoptical system to the light diffuser is expressed by Sin⁻¹(NA). Assumingthat a full angle of a light diffusing angle of the light diffuser is θ,a further divergence angle of θ/2 is added, and thereby a divergenceangle of light rays is expressed by θ/2+Sin⁻¹(NA). Accordingly, if alength between the light diffuser and the spatial light modulator is L,a divergence of the ray of light on the spatial light modulator can beexpressed by 2×tan(θ/2+Sin⁻¹(NA))×L. By setting a half of a lightdivergence on the spatial light modulator smaller than one-third (i.e.,D/3) of the diagonal distance of the image display area of the spatialmodulator, the amount of light not entering the spatial light modulator(loss in the light amount) can be suppressed to 75% or lower.Accordingly, an image projected to the predetermined plane on a screenand the like can be recognized without sense of discomfort.

(4) A laser image display apparatus according to the laser image displayapparatus in any one of (1) to (3), wherein it is preferable that thelight diffusing elements move, sway or oscillate in response to avoltage applied to the light diffuser. According to this construction, asubstance which can be moved swayed or oscillated by applying a voltageis used as a light diffusing element. One example of a substance of thiskind is a particle including TiBaO₃ and the like which is able toundergo induced polarization. Here, for example, if an alternatingvoltage is applied to the light diffuser, migration particles can bemoved, swayed or oscillated in response to modulated frequencies of thevoltage. That is to say, a speckle pattern of the rays of light diffusedby the light diffuser can be changed variously in response to themodulated frequencies of the voltage, and thereby a speckle noise can bereduced effectively.

(5) A laser image display apparatus according to the laser image displayapparatus in (4), wherein it is preferable that the light diffuser has aplurality of electrodes, and a movement of the light diffusing elementsis controlled by a voltage applied to each of the plurality ofelectrodes. According to this construction, for example, an alternatingvoltage is applied individually to a plurality of electrodes which thelight diffuser includes. As a result, a different electric field isgenerated respectively among each of the electrodes, and thereby amovement of the light diffusing elements affected by the electric fielddiffers among each of the electrodes. That is to say, for example, aspeckle pattern of light diffused by the light diffuser can be changedin various ways in response to the modulated frequencies appliedindividually to the plurality of electrodes. Accordingly, a specklenoise can be reduced more effectively. Further, at this time, a movementof the light diffusing elements can be changed in more complicated wayby adjusting an arrangement of the electrodes in such a way where anelectric field is not applied in a parallel direction but being crossed.Accordingly, a speckle noise can be reduced more effectively.

(6) A laser image display apparatus according to the laser image displayapparatus in any one of (1) to (3), wherein it is preferable that thelight diffusing elements move, sway or oscillate in response to a heatapplied to the light diffuser. According to this construction, it is notnecessary to apply electricity or polarize the light diffusing elements,and the light diffusing elements can be moved swayed or oscillatedwithout use of any objects. Further, since a movement such as movingspeed of the light diffusing elements can also be changed variously byheat applied thereto. Accordingly, a speckle noise can be reducedeffectively.

(7) A laser image display apparatus according to the laser image displayapparatus in any one of (1) to (3), wherein it is preferable that thelight diffusing elements move, sway or oscillate in response to a soundwave applied to the light diffuser. According to this construction, itis not necessary to apply electricity or polarize the light diffusingelements, and the light diffusing elements can be moved swayed oroscillated without use of any objects. Further, for example, if a soundwave having a modulated frequency which can be controlled is used, aspeckle pattern of the rays of light diffused by the light diffuser canbe changed variously by the modulated frequency. Accordingly, a specklenoise can be reduced effectively.

(8) A laser image display apparatus according to the laser image displayapparatus in any one of (1) to (3), wherein it is preferable that thelight diffusing elements move, sway or oscillate in response to amagnetic field applied to the light diffuser. According to thisconstruction, a substance which can be moved, swayed or oscillated byapplying a magnetic field is used as a light diffusing element. As suchsubstance, particles made of various sorts of ferromagnetic substance orferromagnetic substance can be used. Here, for example, if a modulatedmagnetic field generated by applying an alternating voltage to a coil isapplied as a magnetic field to the light diffuser, the light diffusingelements can be moved, swayed or oscillated in response to the modulatedfrequencies of the applied voltage. That is to say, since a specklepattern of the diffused light can be variously changed by the modulatedfrequencies of the voltage for generating a magnetic field, a specklenoise can be reduced effectively.

(9) A laser image display apparatus according to the laser image displayapparatus in any one of (1) to (3), wherein it is preferable that thelight diffusing elements are contained with a solvent, and the solventmoves, sways or oscillates. According to this construction, in the lightdiffuser, the solvent contained with the light diffusing elements moves,sways or oscillates. Accordingly, the light diffusing elements moves inresponse to a movement of the solvent even though the light diffusingelements are not directly moved, and thereby a speckle pattern of therays of light diffused by the light diffuser differs at each moment. Asa result, a high quality two-dimensional image having suppressed specklenoise can be obtained.

(10) A laser image display apparatus according to the laser imagedisplay apparatus in any one of (1) to (9), wherein it is preferablethat the light diffusing elements include two or more kinds ofsubstances having different features from one another. According to thisconstruction, the light diffusing elements include two or more kinds ofsubstances having different features such as polarization, size, mass ordensity. For example, in the case where particles have differentpolarization, if a voltage is applied to the light diffuser, movement ofthe light diffusing elements as a whole can be changed in morecomplicated state since each of two or more kinds of have differentmoving speed from one another. Accordingly, various speckle patterns aregenerated, and thereby a high quality two-dimensional image havingsuppressed speckle noise can be obtained.

(11) A laser image display apparatus according to the laser imagedisplay apparatus in any one of (1) to (5), wherein it is preferablethat the light diffusing elements include two or more kinds of liquidcrystals having different polarizations from one another. According tothis construction, each of two or more kinds of liquid crystals havingdifferent polarizations from one another differs in a response speedfrom one another at the time when an electric field is applied.Accordingly, a diffusing pattern of rays of light in the light diffuserbecomes various and many speckle patterns are formed, and thereby it iseffective in speckle noise reduction.

(12) A laser image display apparatus according to the laser imagedisplay apparatus in any one of (1) to (10), wherein it is preferablethat the light diffusing elements include two or more kinds of particleshaving different polarizations from one another. According to thisconstruction, each of two or more kinds of particles having differentpolarization from one another differs in a response speed and the likefrom one another at the time when an electric field is applied.Accordingly, a diffusing pattern of rays of light in the light diffuserbecomes various and many speckle patterns are formed, and thereby it iseffective in speckle noise reduction.

(13) A laser image display apparatus according to the laser imagedisplay apparatus in any one of (1) to (12), wherein it is preferablethat the light diffuser is integrated with the spatial light modulator.According to this construction, in the case where the light diffuser andthe spatial light modulator are attached firmly to each other to beintegrated, amount of rays of light diffused by the light diffuser andnot irradiated to the spatial light diffuser can be suppressed to aminimum. Further, in the case where the light diffuser and the spatiallight modulator are integrated with a predetermined distance kepttherebetween, amount of rays of light not irradiated to the spatiallight diffuser and, further, deterioration of an image quality caused byirregularities of a transmitted ray of light on the spatial lightmodulator can be suppressed. In any cases, a relative displacementbetween the light diffuser and the spatial light modulator caused byvibration and the like can be suppressed. Accordingly, a deteriorationcan be suppressed.

(14) A laser image display apparatus according to the laser imagedisplay apparatus in (13), wherein it is preferable that the spatiallight modulator executes light modulation by a liquid crystal. Accordingto this construction, since an orientation of a liquid crystal can beeasily controlled in response to an input image signal providedelectrically, intensity modulation can be executed effectively.

(15) A laser image display apparatus according to the laser imagedisplay apparatus in (14), wherein it is preferable the spatial lightmodulator executes light modulation by a reflective liquid crystal.According to this construction, since an incident ray of light to thespatial light modulator does not pass through a liquid crystal, a brightimage having small loss in the light amount can be displayed.

(16) A laser image display apparatus according to the laser imageapparatus in any one of (1) to (15), wherein it is preferable that: thelaser light source comprises a laser light source emitting a ray of redlaser light, a laser light source emitting a ray of blue laser light,and a laser light source emitting a ray of red laser light, the rays oflaser light emitted from the laser light sources are combined to asingle ray of laser light after being passed through the lightdiffusers, the illumination optical systems and the spatial lightmodulators which are arranged with the respective laser light sources,and the projection lens projects the combined laser light to apredetermined plane in space.

According to this construction, each of the three laser light sources ofRGB colors (R: Red, G: Green, B: Blue) includes the light diffuser, theillumination optical system and the spatial light modulator. The rays oflight emitted from the three laser light sources are irradiated to thelight diffuser by the illumination optical system respectively. Sincethe light diffusing elements which are moved, swayed or oscillated arecontained in the light diffuser, different speckle patterns occur ateach moment. After the rays of light of three RGB colors having beenpassed through the spatial light modulator are combined to a single rayof laser light, the combined ray of light is projected to thepredetermined plane in space. According to this, a laser image displayapparatus capable of displaying a bright color image with suppressedspeckle noise can be realized.

The present invention is described in detail; however, the descriptionsabove are exemplification of the present invention in all of theaspects, and the present invention is not limited to them. Indefinitenumbers of modified examples may be envisioned within a scope of thisinvention.

INDUSTRIAL APPLICABILITY

The laser image display apparatus of the present invention serves as alaser image display apparatus comprising a means for reducing a specklenoise which appears on a display. The laser image display apparatuscomprises one laser light source and a light diffuser in which lightdiffusing elements are contained so that a speckle noise can be reducedor eliminated by executing a light diffusion to rays of laser lightwithout using a oscillating system such as screen, and thereby a brightimage having no fine and irregular noise can be projected to a screen.Further, an optical system including a light diffuser is set in the mostappropriate position so that loss of light amount after being executed alight diffusion is minimized, and thereby a bright and high-qualityimage having no luminosity irregularity can be realized.

1-16. (canceled)
 17. A laser image display apparatus comprising: a laserlight source; a light diffuser containing light diffusing elements, thelight diffusing elements moving, swaying or oscillating; an illuminationoptical system which irradiates rays of light from the laser lightsource to the light diffuser; a spatial light modulator which isarranged near the light diffuser and irradiated by rays of lightdiffused by the light diffuser to produce image; and a projection lenswhich projects to a predetermined plane in space an image produced bythe spatial light modulator, wherein a light diffusing angle 0 of thelight diffuser, a pitch P of transmission irregularity generated in thelight scattering means, a numerical aperture NA of the illuminationoptical system, and a distance L between the spatial light modulator andthe light diffuser have a relationship of P<2×tan(θ/2+Sin⁻¹(NA))×L. 18.A laser image display apparatus according to claim 17, wherein a lightdiffusing angle θ of the light diffuser, a numerical aperture NA of theillumination optical system, a distance L between the spatial lightmodulator and the light diffuser and a diagonal screen size D of thespatial light modulator have a relationship of tan(θ/2+Sin⁻¹(NA))×L<D/3.19. A laser image display apparatus comprising: a laser light source; alight diffuser containing light diffusing elements, the light diffusingelements moving, swaying or oscillating; an illumination optical systemwhich irradiates rays of light from the laser light source to the lightdiffuser; a spatial light modulator which is arranged near the lightdiffuser and irradiated by rays of light diffused by the light diffuserto produce image; and a projection lens which projects to apredetermined plane in space an image produced by the spatial lightmodulator, wherein a light diffusing angle θ of the light diffuser, anumerical aperture NA of the illumination optical system, a distance Lbetween the spatial light modulator and the light diffuser and adiagonal screen size D of the spatial light modulator have arelationship of tan(θ/2+Sin⁻¹(NA))×L<D/3.
 20. A laser image displayapparatus according to claim 17, wherein the light diffusing elementsmove, sway or oscillate in response to a voltage applied to the lightdiffuser.
 21. A laser image display apparatus according to claim 20,wherein the light diffuser has a plurality of electrodes, and movementof the light diffusing elements is controlled by a voltage applied toeach of the plurality of electrodes.
 22. A laser image display apparatusaccording to claim 17, wherein the light diffusing elements move, swayor oscillate in response to a heat applied to the light diffuser.
 23. Alaser image display apparatus according to claim 17, wherein the lightdiffusing elements move, sway or oscillate in response to a sound waveapplied to the light diffuser.
 24. A laser image display apparatusaccording to claim 17, wherein the light diffusing elements move, swayor oscillate in response to a magnetic field applied to the lightdiffuser.
 25. A laser image display apparatus according to claim 17,wherein the light diffusing elements are contained with a solvent, andthe solvent moves, sways or oscillates.
 26. A laser image displayapparatus according to claim 17, wherein the light diffusing elementsinclude two or more kinds of substances having different features fromone another.
 27. A laser image display apparatus according to claim 17,wherein the light diffusing elements include two or more kinds of liquidcrystals having different polarizations from one another.
 28. A laserimage display apparatus according to claim 17, wherein the lightdiffusing elements include two or more kinds of particles havingdifferent polarizations from one another.
 29. A laser image displayapparatus according to claim 17, wherein the light diffuser isintegrated with the spatial light modulator.
 30. A laser image displayapparatus according to claim 29, wherein the spatial light modulatorexecutes light modulation by a liquid crystal.
 31. A laser image displayapparatus according to claim 30, wherein the spatial light modulatorexecutes light modulation by a reflective liquid crystal.
 32. A laserimage display apparatus according to claim 17, wherein: the laser lightsource comprises a laser light source emitting a ray of red laser light,a laser light source emitting a ray of blue laser light, and a laserlight source emitting a ray of red laser light, the rays of laser lightemitted from the laser light sources are combined to a single ray oflaser light after being passed through the light diffusers, theillumination optical systems and the spatial light modulators which arearranged with the respective laser light sources, and the projectionlens projects the combined laser light to a predetermined plane inspace.
 33. A laser image display apparatus according to claim 19,wherein the light diffusing elements move, sway or oscillate in responseto a voltage applied to the light diffuser.
 34. A laser image displayapparatus according to claim 19, wherein the light diffusing elementsmove, sway or oscillate in response to a heat applied to the lightdiffuser.
 35. A laser image display apparatus according to claim 19,wherein the light diffusing elements move, sway or oscillate in responseto a sound wave applied to the light diffuser.
 36. A laser image displayapparatus according to claim 19, wherein the light diffusing elementsmove, sway or oscillate in response to a magnetic field applied to thelight diffuser.
 37. A laser image display apparatus according to claim19, wherein the light diffusing elements are contained with a solvent,and the solvent moves, sways or oscillates.
 38. A laser image displayapparatus according to claim 19, wherein the light diffusing elementsinclude two or more kinds of substances having different features fromone another.
 39. A laser image display apparatus according to claim 19,wherein the light diffusing elements include two or more kinds of liquidcrystals having different polarizations from one another.
 40. A laserimage display apparatus according to claim 19, wherein the lightdiffusing elements include two or more kinds of particles havingdifferent polarizations from one another.
 41. A laser image displayapparatus according to claim 19, wherein the light diffuser isintegrated with the spatial light modulator.
 42. A laser image displayapparatus according to claim 19, wherein: the laser light sourcecomprises a laser light source emitting a ray of red laser light, alaser light source emitting a ray of blue laser light, and a laser lightsource emitting a ray of red laser light, the rays of laser lightemitted from the laser light sources are combined to a single ray oflaser light after being passed through the light diffusers, theillumination optical systems and the spatial light modulators which arearranged with the respective laser light sources, and the projectionlens projects the combined laser light to a predetermined plane inspace.